Control system



Oct. 10, 1950 R, M, JQLLY 2,525,489

CONTROL SYSTEM Filed Nov. 19, 1948 Lood wlTNEssEsz rLrUULn lNvENToR Patented Oct. 10, 1950 UNITED STATES PATENTv OFFICE I i 2,052'51489 i A CONTROL SYSTEM a Robert M. Jon-y, Pittsburgh, Pa., assignor o'westinghouseElectric Corporation, East Pittsburg Pa., a. corporation of `lennsylvania Application November 19, 1948, Serial No. 60,968

This-invention relates generallyito electrical if* across eonductors |0. fFor this purpose a motor 26 is disposed v`to directionally operated to actuate the tap changer 22 in a predetermined o manner depending upon the selective energiza- In such cases it is necessary to circuits with a'resulting drain on the power sysw tems.

An object lof this invention is to provide for `minimizing or preventing vthe flow of reactive power in a tie line connected 'between two power systems.

VAnother objectof this invention is the provision of [an electronic control'responsive to an unbalance of voltage between two power systems connected by a tie line Vfor changing the input to one of the'systems to 'equalize thevoltage'thereof and prevent or minimize the fiow ofV reactive i power in the tie line'between the power, systems,

i Other objects of this invention will become apparent from the following description when taken in 'conjunction with the accompanying drawing, the single figure of whichl is a d iagrammatic view 'of' apparatus and circuits embodying the teachings of this invention.

` Referring to the'dra'wingV there is illustrated a power system represented by conductors disposed to supply electrical apparatus |2 and connected through a large capacity transformer |4 to be supplied from a power source represented by conductors IB. The power source |6 also Supplies apower system represented by conductors |8 through'aJ tapped transf'ormer 20, the connections of which are disposed to be ad- 'justed by a suitable tap changer represented by -the rectangle 22. Both of the power systems |0 and |8 are disposed to |be maintained at sary to adjust lthe eonnectionsl of the tapped transformer 20 to maintain the voltage across conductors IB at the same value as the voltage tion of the field'pwindings 28 and 30 of the motor 26. 1 I

In order to control the selective energization of the field 'windings 28 and 30, provision is made to obtain a pair oflow ampere directcurrent voltages which constitute measures of the voltages across the `pair of power systems. Thus fa transformer 32 is connected across the power system `IB to supply a full wave dry type rectifier 34, the outputv terminals of which are connected acrossaresistor 3,6 whereby the voltage drop across resistor 36 lconstitutes a measure of the voltageiacross the power system 18. Similarly,v atransformer 38 is connected across the power system |0 for supplying a full'waveV dry type rectifier 40, the output terminals of -which are 'connected lacrossja resistor 42 whereby the voltage 'drop i across resistor I42 constitutes a measure of the voltagelacross the power system IO, As illustrated theresistors 36 and 42 are connected in series circuit relation but with the voltages thereacross in opposition whereby the voltage summati'on thereacross constitutes the differential ofV thetwo 'direct-current voltages i and has` a pOIaritydepending upon whichof the direct-current voltages is the larger.

In orderlto amplify the signal voltage which is the'differential of the direct-current voltages appearing across 'the series connected resistors 36 and 42, a vacuum tube 44 is utilized. The vacuum tube 44 is of usual construction being provided with an anode 46,' a cathode 40 and a control grid 50, the tube 44 being operated as a self-biased tube witha biasing resistor 52 being adjusted for a desired Operating point, at which point current flows in the anode-cathode circuit from a source ofl supply represented by the battery 54. The bias of the control grid is controlled by the voltage ,across the series connec'ted resistors 36 and 42 which are connected in the grid-cathode circuit extending from the grid 50 through resistor 56, series connected resistors 36 and 42 and the self-biasing resistor 52 to the cathode 4,8.

The anode-cathode circuit of the tube 44 extends from the anode 46 through a potentiometer resistor 56, resistor 66, battery 54 across which a potentiometer resistor 62 is connected and the self-biasing resistor 52 to the cathode 48. From the current ow in the anode-cathode Circuit of valve 44 by reason of the self-biasing of the tube, it is seen that the polarity of the voltages across resistors 58 and 60 are in opposition to the polarity of the voltage across the potentiometer resistor 62 which is connected across the battery 54.

As illustrated, a vacuum tube 64 is connected to control the selective energization of a pair of contactors 66 and 68 which control the selective energization of the field windings 28 and 30, respectively, of the motor 26. In this instance, the tube 64 comprises twin anodes and 12, control grids T4 and 16 and a cathode 18 disposed for operation to selectively connect the energizing windings 60 and 82 of contactors 66 and 68, respectively, to a source of supply represented by the battery 84.

The control grid 14 is connected through resistor 86 and a part of the potentiometer resistor 58 to the cathode 18, whereas the grid 16 is connected through resistor 88, a part of potentiometer resistor 62, and resistor 66 to the cathode 16. In practice the potentiometers 58 and 62 are so adjusted when the tube 44 is Operating as a self-biased tube, that the grids 14 and 16 are negatively biased to prevent either of the anode-cathode circuits of tube 64 from conducting. This will be appreciated when it is noted that the potentiometer 58 is connected to supply a negative bias to the grid 14 and that the resistor 60 and potentiometer 62 are connected in the biasing Circuit of grid 16 whereby the resistor 66 Supplies a positive bias and the potentiometer 62 Supplies a negative bias.

In operation, with the potentiometer resistors 56 and 62 adjusted as described to cause a negative bias to be impressed upon the grids 14 and 76, respectively, if the voltage across the power system H] should become high relative to that across the power system |8, then the differential of the opposed direct-current voltages across resistors 36 and 42 will besuch as to apply a positive bias to the grid 56 to increase the conductivity of the tube 44. As the current flow in the anodecathode Circuit thereof increases, the voltage drop across the potentiometer resistor 58 increases whereby the negative bias applied to the grid T4 is increased to prevent the anode-cathode circuit of the tube 64 controlled thereby from conducting. At the same time the voltage drop across resistor 66 is increased whereby the resistor 60 will supply sufiicient positive bias to the grid 'E6 in opposition to the negative bias of potentiometer 62 to render the anode-cathode Circuit of tube 64 controlled thereby conducting. This circuit extends from the anode 12 through the energizing winding 82 of the contactor 68, conductor 65 and the battery 84 to the cathode 78.

When the contactor 68 is thus energized, it is actuated to establish the energizng circuit for the field winding 36 of the motor 26 to effect an operation of the motor in a direction to operate the tap changer 22 to change the connections of the transformer 20 to increase the Voltage across the power system |8 to the value of the voltage across the power system IO.

If on the other hand the voltage across the power system li! should decrease below the voltage across the power system 18, then the differential of the opposed direct current voltages across the series connected resistors 36 and 42 will be such as to apply a less positive bias to the grid 56 to decrease the conductivity of the tube 44. As the current fiow in the anode-cathode circuit of tube 44 decreases the voltage drop across the potentiometer resistor 53 and across resistor 66 decreases. The bias applied to the grid 14 of the tube 64 thus becomes less negative and the anode-cathode Circuit controlled thereby becomes conducting. At the same time, the decrease in the voltage drop across resistor 60 decreases the positive bias applied therefrom in opposition to the negative bias from the potentiometer 62 whereby the bias applied to the grid 'E6 of the tube 64 is so negative as to prevent the anodecathode Circuit controlled thereby from becoming conducting.

When the anode-cathode Circuit controlled by the grid 14 be'comes conducting, the winding of the contactor 66 is energized, the energizing circuit thereof extending from the anode 10 through the winding 86, conductor 96 and the battery 84 to the cathode 18. When thus energized, the contactor 66 establishes the energizing circuit for the field winding 28 of the motor 26 to effect the operation thereof in a direction to drive the tap changer 22 to so change the connections of the transformer 20 as to decrease the voltage across the power system IO to equal the voltage of the power system lfl.

The control system described is very Sensitive and is of particular valueY in maintaining the voltage of the two power systems substantially equal. The advantages of utilizing the low ampere direct-current voltage signals are apparent especially when it is considered that the power systems are usually separated by three or more miles. With this system telephone or other low power circuits can be utilized in transmitting the measuresof the voltage of the power systems, the tube circuits being responsive to minute signals.

In practice, the,contactors 66 and 68 have time delaycharacteristics, as. indicated by the spring attachment 82 therefor whereby momentary fluctuations orfdi'fferences in. the voltages of the power systems will not effect an operation of the tap changing mechanism. If the differences between the vVoltages are sustained, then the system is effective to equalize the voltages and prevent the flow of Vreactive power in the tie line.

I claim las my invention:

1. In a system for limiting the flow of reactive power in a tie line connected lbetween two power systems one of which is connected through a tap changing transformer to a high voltage power source, the combination comprising, means including low power conductors from the power systems for providing a pair of direct current control Voltages constituting measure of the voltages of the two power systems, a vacuum tube having a conductivity dependent upon the differential of said pair of direct current control voltages, another tube having a pair of anode-cathode circuits disposed to be selectively rendered conducting depending upon the conductivity of said first tube, and means disposed to be selectively controlled in response to the selectively conducting pair of anode-cathode circuits to effectran operation of the tap changing transformer to adjust the voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a fiow of reactive power in the tie line therebetween.

asa-5,489

4the'tap changing transformer, a pair of control windings disposed to be selectively energized to control the operation of said means, a vacuum tube means disposed to connect the control windings to a source of energy, the vacuum tube means having twin anodes, grids and a cathode disposed for operation to selectively control the connecting of the pair of control windings, another tube means having an anode and cathode connected in circuit relation with the twin grids to control the bias thereof, a control grid for said another tube means, means including low power conductors from the power systems for providing a pair of opposed direct current voltages that are measures of the voltages of the two power systems, and means connecting the pair of opposed direct current voltages to the control grid of said another tube means whereby the control grid is biased in accordance with the differential of the pair of opposed direct current voltages.

3. In a system for limiting the flow of reactive power in a tie line connected between two power systems one of which is connected through a tap changing transformer to a highV voltage power source, the combination comprising, means including low power conductors from the power systems for providing a pair of low ampere direct current control voltages constituting measures of the voltages of the two power systems, a first vacuum tube having a control grid, means for connecting the control grid to be biased in response to the differential of said pair of control voltages to control the conductivity of said first vacuum tube, another tube having twin anodes, grids and a cathode, means connected in circuit relation with the grids of said another tube and responsive to the conductivity of said first vacuum tube for selectively controlling the conductivity of the twin anode-cathode circuits of said another tube, and means disposed to be selectively Controlled in response to the selective conductivity of the twin anode-cathode circuits to effect an operation of the tap changing transformer to adjust the voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a flow of reactive power in the tie line therebetween.

4. In a system for limiting the flow of reactive power in a tie line connected between two power systems one of which is connected through a tap changing transformer to a high voltage power source, the combination comprising, means including low power conductorsfrom the power systems for providing a pair of direct current control voltages constituting measures of the voltages of the two power systems, a vacuum tube having a conductivity dependent upon the differential of said pair of direct current control voltages, another tube having a pair of anode-cathode circuits disposed to be selectively rendered conducting depending upon the conductivity of said first tube, a pair of contactors disposed to be selectively operated depending upon the selective conductivity of the pair of anode-cathode circuits, and a motor disposed for directional operation in response to the selective operation of the contactors to directionally operate the tap changing transformer to adjust the voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a flow of reactive power in the tie line therebetween.

5. In a system for limiting the fiow of reactive power in a tie line connected between two power systems onev of which is connected through a tap changing transformerv to a high vvoltage power source, the combination comprising, means including low power conductors from the power systems forl providing a pair of low ampere direct current Vcontrol voltages constituting measures of the voltages of the two power systems, a first vacuum tube having a control grid, means for connecting the control grid to be biased in response to the differential of said pair of control voltages to control the conductivity of said first vacuum tube, another tube having twin anodes, grids and a cathode, means connected in circuit relation with the grids of said another tube and responsive to the conductivity of said first vacuum tube for selectively controlling the conductivity of the twin anode-cathode circuits of `said another tube, a pair of contactors disposed to be selectively operated depending upon the selective conductivity of the twin anodecathode circuits of said another tube, and means responsive to the selective operation of the pair of contactors disposed to directionally operate the tap changing transformer to adjust the voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a flow of reactive power in the tie line therebetween.

6. In a system for limiting the fiow of reactive power in a tie line connected between two power systems one of which is connected through a tap changing transformer to a high voltage power source, the combination comprising, means including low power conductors from the power systems for providing a pair of direct current control voltages constituting measures of the voltages of the two power systems, a vacuum tube having a conductivity dependent upon the differential of said pair of direct current control voltages, another tube having a pair of anodecathode circuits disposed to be selectively rendered conducting depending upon the conductivity of said first tube, a pair of contactors disposed to be selectively operated depending upon the selective conductivity of the pair of anodecathode circuits, time delay means associated with each of the contactors to prevent premature operation thereof, and a motor disposed for directonal operation in response to the selective operation of the contactors to directionally operate the tap'changing transformer to adjust the voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a fiow of reactive ,power in the tie line therebetween.

'7. In a ,system for limiting the fiow of reactive power in a tie line connected between two power systems one of which is connected through a, tap changing transformer vto a high voltage power source, the combination comprising, means including low power conductors from the power systems for providing a pair of low ampere direct current control voltages constituting measures of the voltages of the two power systems, a first vacuum tube having a control grid, means for connecting the control grid to be biased in response to the differential of said pair of control voltages to control the conductivity of said first vacuum tube, another tube having twin anodes, grids and a cathode, means connected to prevent premature operation thereof, and 10 means responsive to the selective operation of the pair of contactors dsposed to directionally operate the tap changing transformer to adjust the Voltage of the power system supplied thereby to correspond to the voltage of the other power system and prevent a ow of reactive power in the tie line therebetween.

ROBERT M. JOLLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number i Name Date 2,323,716 Lennox July 6, 1943 2,473,457 Tyson June 14, 1949 

